Weed Management for Parks and Open Lands

The Larimer County Department of Natural Resources weed workgroup manages invasive plant species on over 30,000 acres in 27 parks and open lands. Invasive, non-native plants are known as noxious weeds and most are listed under the Colorado Noxious Weed Act. Noxious weeds threaten the ecological integrity, visitor usability of natural areas and negatively impacts the economy. Noxious weeds adapt easily to different eco-systems, displace native plant communities and wildlife and can potentially thrive in Larimer County. Weed specialists take an integrated management approach to contain and control these invasive exotic plants. By incorporating various methods of control and suppression, the long term management of invasive plants is more successful and sustainable. Individual integrated weed management plans are devised, implemented, monitored, and then revised for each of the parks and open lands properties:

Carter Lake is a reservoir tucked into the foothills west of Loveland, CO. The reservoir is a part of the Colorado-Big Thompson project - a system of reservoirs, tunnels and ditches that provide water from the western slope to communities, hydro-electrical plants and farmers east of the continental divide. The water is managed by the Bureau of Reclamations and the Northern Colorado Water Conservancy District. Land surrounding Carter Lake is managed by the Larimer County Department of Natural Resources. The park itself is 1,000 acres of shrubland and forest . Canada thistle, musk thistle, myrtle spurge and yellow toadflax are noxious weeds of concern in the area.

Herbicide applications targeting the thistle species below the dams have been successful. Monitoring and weed mapping has revealed a significant decrease in both Canada thistle and musk thistle.

In 2011 Larimer County staff hosted a Pulling for Colorado event to create awareness of escaped ornamental plant species and help neighbors in the area identify and dispose of these exotic invaders. The primary species of concern was myrtle spurge, a tap rooted, perennial plant that can easily escape flowerbeds and infest surrounding areas.

The Devil's Backbone Open Space is west of Loveland on Highway 34. The topography transforms from flat prairie to steep cliffs and hogbacks. The native vegetation includes perennial grasses, forbs and shrubs. The noxious weeds present include: Canada thistle, downy brome, kochia, musk thistle and Russian thistle. Weed management on the Devil's Backbone ranges from weed whacking musk thistle and kochia to making selective herbicide applications.

On the Indian Creek portion of the Devil's Backbone the site appears to have been heavily impacted by domestic livestock grazing prior to the county's acquisition, resulting in a plant community dominated by downy brome and Japanese brome (both plants are also known as 'cheatgrass').

In 2007, Larimer County Department of Natural Resources began to restore the native plant community in the Indian Creek valley. A variety of management tools, used to suppress large portions of cheatgrass, began shifting plant community dominance back to native perennial grass species.

Staff began the restoration process with the controlled burn of a 40 acre tract in October 2007. The standing dead stalks (or thatch) serve as fuel to carry the fire and generate enough heat to kill newly emerged green cheatgrass at ground level. Cheatgrass seed, imbedded in the thatch layer at ground level, typically survives the burn.

Subsequent flushes of cheatgrass following a fall burn occurred at this site in November 2007. At the first opportunity, herbicide was applied across the burn area for selective control of the second flush.

In the spring a 40 acre section of cheatgrass further north on Indian Creek was similarly managed. A spring burn can be more effective than in the fall because a subsequent flush of cheatgrass will not occur after the fire. However, winter moisture often prevents spring fires from burning as thoroughly.

Sheep grazing was utilized in April of 2008 for cheatgrass suppression on the west side of the service road. Approximately 1000 sheep grazed a five acre area. A second grazing was planned for May, but the presence of bighorn sheep in the vicinity put an end to domestic sheep grazing. It was feared that the domestic animals could potentially spread lungworm to the bighorns. The overgrazing of sheep in such a small area at the Devil's Backbone created a large amount of soil disturbance and later brought an onslaught of common mullein.

For the areas within the Indian Creek Valley that is inaccessible to ground equipment, a helicopter was brought in to apply herbicide in October 2010. Another helicopter application is planned for the spring of 2012 to address the growing feral rye problem on the west side. Future prescribed burns are also in the works for 2012.

Transect monitoring has revealed significantly less cheatgrass at the Devil’s Backbone as a direct result of the weed management that has taken place to date.

Eagle's Nest Open Space is 755 acres south of Livermore. The topography varies greatly from rolling grasslands - to foothills - to large hanging cliffs. Riparian habitat is found along the North Fork of the Poudre River running through the middle of the property. Native vegetation includes grasslands, mountain mahogany shrub lands, and ponderosa pine woodlands. Pastures are leased to ranchers for cattle grazing. The grazing often improves rangeland health on the property, benefiting native plants when the correct stocking rate is used.

Noxious weed management has been ongoing and arduous at times since the purchase of the property in 2001. However, significant reduction in invasive plant species has been achieved. Noxious weeds of concern at Eagle's Nest include: Canada thistle, Dalmatian toadflax, cheatgrass, leafy spurge, musk thistle and Russian thistle. Leafy spurge can only be effectively controlled with herbicide due to it's deep roots and rhizomes. Dalmatian toadflax is also managed with herbicide. These two perennial weeds are especially challenging because of such vigorous growth.

The Larimer County weed work group is currently looking into releasing mecinus janthinus, an insect bio-control agent that targets Dalmatian toadflax, onto the steep and inaccessible hills at Eagle's Nest to the west of the river.

Much progress has also been made in re-vegetating bare areas heavily affected by cattle holding in the same spot for an extended period of time. Temporary electric fences have been built to protect against the cattle returning and congregating.

Flatiron Reservoir is in the foothills, north of Carter Lake and west of Loveland, CO. The reservoir is a part of the Colorado-Big Thompson project - a system of reservoirs, tunnels and ditches that provide water from the western slope to communities, hydro-electrical plants and farmers east of the divide. The water is managed by the Bureau of Reclamations and the Northern Colorado Water Conservancy District. The vegetation around Flatiron Reservoir is managed by Larimer County Department of Natural Resources. The public park surrounding the lake is 200 acres of mountain mahogany shrub lands, native plant communities and campgrounds. Noxious weeds of concern in the area include: Canada thistle, common mullein, diffuse knapweed, moth mullein, musk thistle and Russian olive trees.

Hermit Park is south of Estes Park off of US highway 36. This park's topography varies between rolling mountains and pristine grass meadows. The vegetation is comprised primarily with ponderosa pine woodlands and native grasses. Hermit's Park was purchased by Larimer County Natural Resources in 2007. This park is new to the county therefore, weed specialists are working diligently to scout the entire area and map key weed infestations. Some of the noxious weeds of concern include: Canada thistle, diffuse knapweed, musk thistle and yellow toadflax.

Starting in 2009, diffuse knapweed was targeted for eradication at the main entrance of the park. Today there is only a small amount left on the way into the open space. Larimer County staff is also working cooperatively with neighboring landowners to address this problem, which is already widespread in the Estes Valley.

Horsetooth Mountain Open Space is over 2,700 acres to the west of Horsetooth Reservoir. The topography varies greatly from meadows to cliffs The vegetation consists of ponderosa pine woodlands, mountain mahogany shrublands and a mix of native and exotic pasture grasses. The noxious weeds of concern include: bull thistle, Canada thistle, common mullein, Dalmatian toadflax, leafy spurge, moth mullein, musk thistle and myrtle spurge.

Myrtle spurge, being an A list species, is targeted for eradication in the park. Currently three small infestations are known to exist. Myrtle spurge can be controlled through hand pulling if enough of the root is ripped out of the ground. Leafy spurge is also a large concern due to it's aggressive nature, deep roots and prolific rhizomes.

Besides the use of selective herbicides and mechanical means to control weeds at Horsetooth Mountain, the biological agent, mecinus janthinus, has been released in some areas to target Dalmatian toadflax. Visual observation has revealed mecinus janthinus to be inflicting damage upon Dalmatian toadflax and possibly reducing infestation levels at this open space and surrounding area.

Horsetooth Reservoir is tucked in the foothills to the west of Fort Collins, CO. The reservoir is a part of the Colorado-Big Thompson project - a system of reservoirs, tunnels and ditches that provide water from the western slope to communities, hydro-electrical plants and farmers east of the divide. The water is managed by the Bureau of Land Management and the Northern Colorado Water Conservancy District. The vegetation surrounding Horsetooth Reservoir is managed by Larimer County Department of Natural Resources. The public park surrounding the lake is 2,000 acres of Ponderosa Pine woodlands and mountain mahogany shrublands. Noxious weeds of concern include: bull thistle, Canada thistle, common mullein, dalmatian toadflax, houndstongue, leafy spurge, moth mullein, musk thistle, poison hemlock, tamarisk and yellow toadflax.

Due to steep terrain and the lack of four-wheel drive access to areas that are heavily infested with Dalmatian toadflax, in 2008 weed specialists from Larimer County and APHIS (animal and plant health inspection services) released the insect bio-control mecinus janthinus; a stem boring weevil. The project is a collaborative research effort to research best management practices for the area. In 2011 the area of release was monitored. Significantly less Dalmatian toadflax was at the site. At Horsetooth Reservoir there have also been releases of the aphthona insect; a flea beetle, which targets leafy spurge.

Selective herbicides are also utilized throughout the late spring, summer and fall. When the water level recedes in August, the weed work group uses boats to access the Canada thistle and musk thistle that grow below the high water mark. Selective, aquatic labeled herbicides are then used to diminish the seed banks and control the invasive thistles. Aquatically labeled herbicides are scientifically proven to provide the most effective control without damaging water quality or aquatic wildlife at the recommended rates.

Lion's Open Space is 20 acres outside of Laporte, CO. This day use area serves as a picnic ground, trail head and wildlife area. The Pleasant Valley Trail follows the Poudre River through the property. This riparian area hosts a variety of native vegetation from cottonwood trees and willows to wildflowers and grasses.

The noxious weeds of concern include: Canada thistle, Dalmatian toadflax, field bindweed, and leafy spurge. The abundance of weeds has steadily been decreasing. In recent years management consisted of a couple well timed herbicide applications.

Pinewood Reservoir is north-west of Carter Lake and west of Loveland, CO. The reservoir is a part of the Colorado-Big Thompson project – a system of reservoirs, tunnels and ditches that provide water from the western slope to communities, hydro-electrical plants and farmers east of the divide. The water is managed by the Bureau of Reclamation and the Northern Colorado Water Conservancy District. The vegetation around Pinewood Reservoir is managed by Larimer County Department of Natural Resources. The public park surrounding the lake is 327 acres of ponderosa pine woodlands, mountain mahogany shrublands and native grasslands. Noxious weeds of concern include: Canada thistle, Dalmatian toadflax, common mullein, diffuse knapweed, moth mullein and musk thistle. The state of Colorado "list A" noxious weed myrtle spurge has been found in the subdivision to the north of Pinewood Reservoir. If any park visitor sees myrtle spurge along the trails at Pinewood Reservoir, they are encouraged to report it to Casey Cisneros at (970) 619 4578 or by e-mail at cisnerct@co.larimer.co.us.

Pleasant Valley Trail is managed by Larimer County from the entrance of Watson Lake to the south end of Lions Park near Laporte, CO. The trail moves through a corridor that could provide habitat for the Prebles Meadow Jumping mouse, a federally listed endangered species. To mitigate for Prebles habitat, Larimer County has partnered up with various other organizations to plant shrubs along the path. To protect these new shrubs, noxious weed management is necessary to limit the plant competition in this area. The noxious weeds of concern include: Canada thistle, common mullein, kochia, leafy spurge, musk thistle and Russian knapweed. Herbicide applications are made in the late spring and fall. Some of the invasive annuals and biennials are effectively controlled with shovels and weed whackers.

Ramsay-Shockey Open Space is 177 acres of sloped hills with ponderosa pine woodlands, mountain mahogany shrubland and native plant communities. Ramsay-Shockey hosts a system of trails that interconnect with the trails at Pinewood Reservoir. The noxious weeds that are of concern include: Canada thistle, common mullein, downy brome, and musk thistle.

Red Mountain Open Space is 14,980 acre area in the Laramie Foothills. The property is part of an effort to preserve the pristine Laramie Foothills, the land between Interstate Highway I-25 and US Highway 287 in northern Colorado. Adjacent to the east of Red Mountain Open Space is Soap Stone Natural Area, which is managed by the city of Fort Collins. To the north of Red Mountain Open Space is an area managed by the city of Cheyenne. The landscape at Red Mountain Open Space changes dramatically within its borders. The vegetation includes ponderosa pine woodlands, native grasslands and mountain mahogany shrublands. Throughout the open space are rare and endangered flora including a native perennial thistle species, Cirsium Flodmanii.

At some of the most remote locations on the open space, researchers from Colorado State University have released 1,800 mecinus janthinus, an insect bio-control, to target Dalmatian toadflax. Mecinus janthinus is a stem boring weevil that naturally feeds on Dalmatian toadflax. The researchers will monitor the establishment of the insect's populations and their impact upon the target plant.

The leafy spurge that is prevalent in one of the main washes near the trailhead is targeted for eradication using a late spring and fall herbicide application. Positive progress managing the leafy spurge has been monitored.

Some of the Russian olive trees and tamarisk/saltcedars have been removed and controlled with a cut-stump application. While more are to be removed in the upcoming season.

Rimrock Open Space is north of the Devil's Back Bone. Several trails, including the Blue Sky Trail, converge on Rim Rock and head off to the north, south and east. The property is 437 acres of gently sloping rangeland, rocky hogbacks, and steep cliffs. The native vegetation on Rim Rock includes grasslands, mountain mahogany shrublands and skunkbush shrublands. Rim Rock is also home to several rare or threatened plant and animal species. The noxious weeds of concern include: Canada thistle, musk thistle and field bindweed. Weed management on Rim Rock include digging musk thistle rosettes and a minimal amount of herbicide applications.

The Soderberg Homestead is 101.5 acres to the west of Inlet Bay at Horsetooth Reservoir. The trail moves north from the trailhead and connects with the Horsetooth Mountain trail system. The native vegetation consists of ponderosa pine woodlands, mountain mahogany shrublands and foothill grasslands. The native grasses are host plants for imperiled butterflies in the area. The noxious weeds of concern include: Canada thistle, common mullein, Downy brome, Dalmatian toadflax, myrtle spurge and yellow toadflax. Management consists of hand pulling the myrtle spurge and minimal herbicide applications.

In 2008 the weed work group found small amounts of yellow toadflax and myrtle spurge (list 'A' species) on the Soderberg homestead. These two plants are targeted for eradication in this area. Because of the early detection and rapid response to these two highly invasive species, their further spread is less likely.

Every property presents unique challenges that must be taken into consideration when developing a weed management plan. For example, in 2008 at Horsetooth Reservoir the steep hills and lack of four wheel drive access made controlling the densely populated Dalmatian toadflax a difficult task. Instead of utilizing herbicides in these areas, weed specialists have had to rely on the release of the insect bio-control mecinus janthinus, a stem boring weevil, to reduce and suppress the number of Dalmatian toadflax.

Once released onto the target site, these insects are monitored over an extended period of time to assure population establishment and impact upon the targeted weed species. If successful, the weevil will eventually reduce the population of toadflax to an acceptable threshold.

Some other invasive plants that the state of Colorado has classified as 'list A' species, which the weed work group is keeping a high level of vigilance for include: Mediterranean sage, orange hawkweed, purple loosestrife and yellow starthistle.

To report the sighting of any 'list A' species or for any question, call the Larimer County Weed District office at (970) 498 5768. Prevention is the greatest tool to protect the natural integrity of the parks and open lands. The cost is less and the benefits far greater if new weed infestations are kept out or controlled early. By understanding what areas are susceptible to weed invasion, how seeds are transported by people/livestock/pets, and how to properly identify weeds, Larimer County citizens and staff can effectively recognize and prevent new weed invaders from appearing on public lands.